| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 106 === This research is to study the flow properties and mixing characteristics of a typical conveying and kneading element in a twin screw extruder via a numerical approach. An unsteady, three-dimensional model is implemented in this study under the assumptions of an isothermal and incompressible flow. By solving the continuity and momentum equation, physical quantities such as strain rate, velocity components and pressure, are obtained. The modified Cross-WLF model is employed to describe the rheological properties of the polymer adopted in this study. The commercial software, STAR-CCM+ is used for the numerical simulation of the twin screw extrusion flow. A Lagrangian description of particle tracing method is developed to predict the trajectory of pseudo particles of the twin screw extrusion flow based on a fourth-order Runge-Kutta method. Three mass flowrate, 10 kg/hr, 20 kg/hr, 40 kg/hr, as well as three screw speed, 75 rpm, 150 rpm, 300 rpm, are adopted to investigate the influence on the both screw elements. Numerical results show that the strain rate in the flow is mainly affected by the screw speed, while the pressure drop is substantially influenced by the mass flowrate. Under the same operation condition, the conveying element has a larger pressure drop when compared to the kneading one. Screw speed has a dominant effect on enhancing dispersion, where reducing the screw speed leads to a better dispersibility. The kneading element has a better dispersive mixing efficiency than the conveying counterpart under the same operation condition. However, the kneading element at high rotational speed and the conveying element at low rotational speed tend to deliver a better distributive mixing performance.
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